A Formula Expressing a General Relationship Between Blood Pressure and Body Weight.

Abstract

The question of a relationship between body weight and blood pressure may be studied from the findings in large numbers of individuals of various sizes essentially normal, particularly as regards the cardiovascular system and nutritional status. Children afford the best material for such a study. In them a large range of body size is available, and arterial disease is so rare that in group studies it can safely be disregarded as a disturbing factor. Satisfactory tables of normal weight or height are at hand for the exclusion of nutritionally unsuitable cases. By utilizing group averages the effects of temporary or accidental variations in pressure, of observational error, and of individual variations in body structure or composition can all be minimized.

The following study is based on observations of about 1,000 approximately normal children, between 4 and 16 years of age, mainly from kindergartens and public schools. By plotting individual blood pressures against body weights∗ it was found that the points of intersection roughly followed a curve of general parabolic form. Dividing the cases into twelve groups by age (without reference to sex) average weights and corresponding systolic and diastolic pressures for each group were determined, with the results shown in Table I. The logarithms of weight when plotted against the logarithms of pressure followed an approximately straight line, from which it was inferred that the relationship between weight and pressure could be expressed by the general formula y=ax^b, or S/D=aW^b. Solving for the six pairs and averaging, the following values for b were found: b_s=0.2055, b_D=0.1900. Assuming a uniform value of 0.2 for b, the average for the constant a was found to be a_s=511.725, or approximately 51.7, a_D=34.730, or approximately 34.7. The formulas derived for systolic pressure and diastolic pressure are therefore S=51.7 W^0.2, D=34.7 W^0.2, and by difference P=17.0 W^0.2, in which S is systolic pressure, D is diastolic pressure, P is pulse pressure, all in millimeters of mercury; and W is body weight in kilograms.